A large number of subterranean wells, including petroleum wells and injection wells, are equipped with various instruments, control devices, operating equipment (for example valves) and similar requiring a supply of electric energy. Typically, such a supply is provided by means of electric cables extending from the surface, or by means of batteries requiring replacement when depleted. Both solutions are associated with great disadvantages.
The use of electric cables contributes large costs and greater technical complexity to the wells. Many errors of such instrumented wells are known to be caused by malfunction in electric cables and/or in electric contacts/connectors for such cables.
A substantial disadvantage of using batteries is the high cost associated with replacement of the batteries. This particularly relates to so-called subsea wells, in which the wellhead is placed on a sea floor. When replacing the batteries in such wells, special vessels (ships or rigs) normally have to be contracted for carrying out maintenance. This is costly and also depends on weather conditions and availability of the vessels.
As a consequence of the abovementioned disadvantages, there is great interest in the industry for technical solutions allowing electric energy to be generated in situ within a well.